Hydrodynamic radial lip seals have been developed to improve performance and durability of rotational contact seals.
Radial lip seals used in relatively rotatable applications are inherently hydrodynamic to a limited extent. Hydrodynamic activity can be increased by incorporating special hydrodynamic aids such as grooves, flutes, ribs or threads adjacent the sealing lip. As seal lips having hydrodynamic aids are rotated, the aids act as small hydrodynamic pumps that direct fluid in contact with the seal lip to the fluid side of the lip. Hydrodynamic elements must be carefully formed and properly installed to be effective.
Hydrodynamic seals are sensitive to eccentricity of the shaft or sleeve. If the seal is eccentric relative to the element against which it seals, hydrodynamic activity may be substantially reduced.
Polytetrafluoroethylene (PTFE) has been proposed as a seal material for rotational contact seals. While hydrodynamic elements may be molded or cut on a PTFE seal lip, frictional wear tends to rapidly neutralize the effect of the hydrodynamic aids.
PTFE wafers are also used as sealing elements by deforming the wafers into a conical configuration. In the conical configuration the PTFE wafer is held with a substantial interference fit against the relatively rotated machine element. PTFE seals having a conical configuration must be carefully installed to prevent scoring the PTFE wafer.
One advantage of PTFE seals is that imperfections in the surface contacted by the seal element may be filled by PTFE being deposited in grooves or indentations. This smooths the surface sealed and tends to improve seal life.
While hydrodynamic seals have improved seal life and performance when properly manufactured and installed, a simple and effective hydrodynamic seal that is easy to manufacture and install has long been needed to permit the use of hydrodynamic seals in conventional and innovative seal applications.